how to push back / repel clothes from a surface?
Go into edit mode with a piece of clothing selected. 

Enable proportional editing by pressing O. Turn on x-ray with AltZ in order to help you see the mesh stuck inside the model more easily.

Select a vertice that is inside the person, pull the vertice out of the character. Adjust the proportional size with your scroll wheel. This will determine how nearby vertices are affected. Repeat with other clothes.